Currently, devices in a circuit may typically give rise to various noises. For studying the regularity of noise, research is generally made on MOS transistor. The MOS transistor may be considered as a micro circuit, including various resistors, capacitors and active devices. For MOS transistor, thermal noise on gate, source and drain, thermal noise and 1/f noise in channel, thermal noise on substrate and inductive noise on the gate, etc. may be involved. The 1/f noise is generally a low frequency noise, and is called like this because the noise increases in inverse proportion to the frequency. The 1/f noise primarily influences devices operating in a low frequency environment. However in some radio frequency circuits, such as frequency mixer, amplifier and frequency divider, etc., the 1/f noise has an increasing influence in high frequency band, and may result in a deteriorated signal-to-noise rate and the like. For circuit design and analysis, it is rather important to have a model that can simulate the noise precisely.
Generally, a conventional device modeling method includes: analyzing obtained data; finding regularity from the data, e.g. a variation according to a voltage or a current; and then finding an equation to describe the regularity with mathematic method. For instance, in a document entitled Device Modeling for Analog and RF CMOS Circuit Design, ISBN 0-471-49869-6, there has been disclosed a model of noise in MOS transistor, which takes some current parameters as primary related factors of noise. For instance, a quadratic drain current is taken as a primary related factor of the 1/f noise in channel of the MOS transistor, and is adapted to construct an equation for describing the variation regularity of the 1/f noise in combination with other factors, such as frequency, capacitance of gate oxidization layer per unit area, channel length, etc., In the circuit design and analysis, some simulation software, such as HSPICE, may be used to simulate noise in the MOS transistor under direct current, alternating current, small signal and instantaneous analysis, etc. The MOS transistor model contained in the simulation software is an MOS transistor library files including noise model files. For noise simulation, noise parameter in the equation for describing noise and variation of the noise parameter configured in a library file generally determine the accuracy of the noise simulation. Thus, in the noise simulation, some noise parameters can be determined from the MOS transistor to be simulated, such as the channel length, while the variation of the noise parameter configured in the library, for instance, are experiential values obtained from practical measurements. At present, most of these experiential values are based upon some measurement data without considering various factors in process. For example, gate oxide growth may cause difference in noise among different wafers, different dies and different runs. When a circuit designer needs to use a MOS transistor noise model to simulate noise for aiding the design, the designer is unable to determine whether the model for the simulation of the noise is sufficiently precise or not, and the design quality may be influenced if a noise model which is not sufficiently precise is applied.